“The body mass index has long been criticized as a flawed indicator of health. A replacement has been gaining support: the body roundness index.” Article unfortunately doesn’t give the freaking formula for chrissakes; it’s “364.2 − 365.5 × √(1 − [waist circumference in centimeters / 2π]2 / [0.5 × height in centimeters]2), according to the formula developed by Thomas et al.10”
Seems like a lot of the flaws just have to do with the fact that the real metrics you want to use, which would probably be body fat percentage, are hard to measure accurately at home.